From: Mel Gorman <mgorman@techsingularity.net>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Michal Hocko <mhocko@suse.com>,
Uladzislau Rezki <urezki@gmail.com>,
Vlastimil Babka <vbabka@suse.cz>,
LKML <linux-kernel@vger.kernel.org>, RCU <rcu@vger.kernel.org>,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Theodore Y . Ts'o" <tytso@mit.edu>,
Joel Fernandes <joel@joelfernandes.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Subject: Re: [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func.
Date: Tue, 6 Oct 2020 11:03:34 +0100 [thread overview]
Message-ID: <20201006100334.GK3227@techsingularity.net> (raw)
In-Reply-To: <20201002144120.GI29330@paulmck-ThinkPad-P72>
On Fri, Oct 02, 2020 at 07:41:20AM -0700, Paul E. McKenney wrote:
> On Fri, Oct 02, 2020 at 11:19:52AM +0100, Mel Gorman wrote:
> > On Fri, Oct 02, 2020 at 11:58:58AM +0200, Peter Zijlstra wrote:
> > > > It's enabled by default by enough distros that adding too many checks
> > > > is potentially painful. Granted it would be missed by most benchmarking
> > > > which tend to control allocations from userspace but a lot of performance
> > > > problems I see are the "death by a thousand cuts" variety.
> > >
> > > Oh quite agreed, aka death by accounting. But if people are enabling
> > > DEBUG options in production kernels, there's something wrong, no?
> > >
> >
> > You'd think but historically I believe DEBUG_VM was enabled for some
> > distributions because it made certain classes of problems easier to debug
> > early. There is also a recent trend for enabling various DEBUG options for
> > "hardening" even when they protect very specific corner cases or are for
> > intended for kernel development. I've pushed back where I have an opinion
> > that matters but it's generally corrosive.
> >
> > > Should we now go add CONFIG_REALLY_DEBUG_STAY_AWAY_ALREADY options?
> >
> > It's heading in that direction :(
>
> Given that you guys have just reiterated yet again that you are very
> unhappy with either a GFP_ flag or a special function like the one that
> Peter Zijlstra put together, it would be very helpful if you were to at
> least voice some level of support for Thomas Gleixner's patchset, which,
> if accepted, will allow me to solve at least 50% of the problem.
>
I read through the series and didn't find anything problematic that
had not been covered already. Minimally, avoiding surprises about what
preemptible() means in different contexts is nice. While I have not
run it through a test grid to check, I'd be very surprised if this was
problematic from a performance perspective on a preempt-disabled kernels.
Last I checked, the difference between PREEMPT_NONE and PREEMPT_VOLUNTARY
was less than 2% *at worst* and I don't think that was due to the preempt
accounting.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2020-10-06 10:03 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-18 19:48 [PATCH 0/4] kvfree_rcu() and _LOCK_NESTING/_PREEMPT_RT Uladzislau Rezki (Sony)
2020-09-18 19:48 ` [PATCH 1/4] rcu/tree: Add a work to allocate pages from regular context Uladzislau Rezki (Sony)
2020-09-18 19:48 ` [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func Uladzislau Rezki (Sony)
2020-09-21 7:47 ` Michal Hocko
2020-09-21 15:45 ` Paul E. McKenney
2020-09-21 16:03 ` Michal Hocko
2020-09-21 19:48 ` Uladzislau Rezki
2020-09-22 7:50 ` Michal Hocko
2020-09-22 13:12 ` Uladzislau Rezki
2020-09-22 15:35 ` Michal Hocko
2020-09-23 10:37 ` Mel Gorman
2020-09-23 15:41 ` Paul E. McKenney
2020-09-23 23:22 ` Mel Gorman
2020-09-24 8:16 ` Uladzislau Rezki
2020-09-24 11:16 ` Peter Zijlstra
2020-09-24 15:16 ` Uladzislau Rezki
2020-09-24 11:19 ` Peter Zijlstra
2020-09-24 15:21 ` Uladzislau Rezki
2020-09-25 8:15 ` Peter Zijlstra
2020-09-25 10:25 ` Uladzislau Rezki
2020-09-24 15:38 ` Paul E. McKenney
2020-09-25 8:26 ` Peter Zijlstra
2020-09-26 14:37 ` Paul E. McKenney
2020-09-25 8:05 ` Michal Hocko
2020-09-25 15:31 ` Uladzislau Rezki
2020-09-25 15:47 ` Michal Hocko
2020-09-29 16:25 ` Uladzislau Rezki
2020-09-30 9:27 ` Michal Hocko
2020-09-30 12:35 ` Uladzislau Rezki
2020-09-30 12:44 ` Michal Hocko
2020-09-30 13:39 ` Uladzislau Rezki
2020-09-30 16:46 ` Michal Hocko
2020-09-30 20:36 ` Uladzislau Rezki
2020-09-30 15:25 ` Joel Fernandes
2020-09-30 16:48 ` Michal Hocko
2020-09-30 17:03 ` Joel Fernandes
2020-09-30 17:22 ` Michal Hocko
2020-09-30 17:48 ` Joel Fernandes
2020-09-25 16:17 ` Mel Gorman
2020-09-25 17:57 ` Uladzislau Rezki
2020-09-22 15:49 ` Paul E. McKenney
2020-09-22 3:35 ` Paul E. McKenney
2020-09-22 8:03 ` Michal Hocko
2020-09-22 15:46 ` Paul E. McKenney
2020-09-23 11:27 ` Uladzislau Rezki
2020-09-29 10:15 ` Vlastimil Babka
2020-09-29 22:07 ` Uladzislau Rezki
2020-09-30 10:35 ` Michal Hocko
2020-10-01 19:32 ` Uladzislau Rezki
2020-09-30 14:39 ` Vlastimil Babka
2020-09-30 15:37 ` Joel Fernandes
2020-10-01 19:26 ` Uladzislau Rezki
2020-10-02 7:11 ` Michal Hocko
2020-10-02 8:50 ` Mel Gorman
2020-10-02 9:05 ` Michal Hocko
2020-10-05 15:08 ` Uladzislau Rezki
2020-10-05 15:41 ` Michal Hocko
2020-10-06 22:25 ` Uladzislau Rezki
2020-10-07 10:02 ` Michal Hocko
2020-10-07 11:02 ` Uladzislau Rezki
2020-10-02 9:07 ` Peter Zijlstra
2020-10-02 9:45 ` Mel Gorman
2020-10-02 9:58 ` Peter Zijlstra
2020-10-02 10:19 ` Mel Gorman
2020-10-02 14:41 ` Paul E. McKenney
2020-10-06 10:03 ` Mel Gorman [this message]
2020-10-06 15:41 ` Paul E. McKenney
2020-10-05 13:58 ` Uladzislau Rezki
2020-10-02 8:06 ` Mel Gorman
2020-10-05 14:12 ` Uladzislau Rezki
2020-09-18 19:48 ` [PATCH 3/4] rcu/tree: use " Uladzislau Rezki (Sony)
2020-09-18 19:48 ` [PATCH 4/4] rcu/tree: Use schedule_delayed_work() instead of WQ_HIGHPRI queue Uladzislau Rezki (Sony)
2020-09-20 15:06 ` Paul E. McKenney
2020-09-21 13:27 ` Uladzislau Rezki
2020-09-18 22:15 ` [PATCH 0/4] kvfree_rcu() and _LOCK_NESTING/_PREEMPT_RT Paul E. McKenney
2020-09-30 15:52 ` Joel Fernandes
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